JP2016119662A - Common-mode noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a common-mode noise filter that overcomes disadvantages in a known noise filter.SOLUTION: The common-mode noise filter comprises first and second inductors which are connected in series between a noise source and a load, and is adapted to be connected in series between the noise source and the load. A capacitor indicating parasitic inductance is connected with a third inductor in series, another end of the third inductor being connected to a junction of the first and second inductors. The first, second and third inductors are selection and positioned each other in such a manner that an absolute value of the third inductor and a result subtracting the parasitic inductance of the capacitor from mutual inductance of the first, second and third inductor are suppressed to a minimum.SELECTED DRAWING: Figure 2

Description

  The present invention relates generally to an in-phase noise filter for electrical systems.

  There are many known electrical systems that have an electrical noise source. Unless electrical noise is eliminated or at least reduced, electrical noise can adversely affect not only the operation of the electrical system itself, but also the associated or surrounding electrical system.

  For example, in an electric vehicle or a hybrid vehicle, a switching power supply or inverter is typically used to generate the voltage necessary to power the vehicle's motor. Traditionally, switching field effect transistors (FETs), GTOs, or IGBTs are used to generate power signals from power supplies. However, in these FETs, a large amount of electrical noise is generated each time the FET switches between an on state and an off state.

  Such systems typically involve two different types of electrical noise that differ from each other in terms of propagation path. First, there is a differential mode current in which current flows through two or more cables in opposite directions relative to the source and load. Second, there is a common mode current that flows in two or more cables in the same direction. This common-mode current is generally high-frequency, and the influence on the outside is greater than the differential noise among the two different types of electrical noise.

  One known method of reducing common mode noise is to utilize a common mode filter, preferably electrically connected to the electrical system in the vicinity of the noise source. These known filters typically comprise a common mode choke coil L and a capacitor connected between each power line of the electrical system and ground. The common-mode choke coil and the capacitor provide a low-pass filter that acts only on the common-mode current.

  However, actual capacitors exhibit parasitic inductance (ESL) that reduces the overall efficiency of the common mode noise filter.

  For example, see FIG. 1, where filter efficiency is plotted on the vertical axis and frequency is plotted on the horizontal axis. Assuming that the noise filter capacitor is an ideal capacitor without parasitic inductances, the filter continuously increases the amount of noise passing through the filter as the noise frequency increases, as shown in graph 10. To reduce. However, since there is no ideal capacitor, graph 12 shows a lower filter efficiency when taking into account the actual capacitor parasitic inductance (ESL). As can be clearly seen from FIG. 1, in the presence of ESL, the amount of common mode noise that passes through the filter increases dramatically.

  A number of known methods are known that reduce the ESL of a filter and thus reduce the amount of common mode noise that passes through the filter. For example, reducing the cable length of the cabling used to connect the filter to ground will reduce the amount of parasitic inductance in the capacitor cable, resulting in reduced ESL. For example, the graph 14 in FIG. 1 shows the filter performance when the cable length of the capacitor is shortened compared to the graph 12 in FIG.

  Yet another way to reduce ESL is to use ESL cancellation. In ESL cancellation, each filter inductor of the common-mode filter is split in two, the two inductors are coupled with each other, and the negative inductance appears at the midpoint of the two connected filter inductors. As a result, capacitance can be added between the midpoint and ground. The inductor is ideally adjusted to zero using the sum of ESL and negative inductance. However, conventional common-mode LC filters that include ESL cancellation use large common-mode choke coils that contain many Ls. As a result, the negative inductance is too large and another coil must be added in series with the capacitive ESL to tune the cancellation. Such a cancellation circuit entails an increase in the overall number, size, and weight of the noise filter. Furthermore, even if the inductance of the capacitor is a very precise inductor, an error in inductance may cause a significant reduction in filter efficiency.

  The present invention provides a common mode noise filter that overcomes the above disadvantages of known noise filters.

  Briefly, the common mode noise filter of the present invention includes first and second inductors connected in series between a noise source and a load, respectively. The inductance of the first inductor is much larger than the inductance of the second inductor.

  The third inductor then has a first end connected to the junction between the first and second inductors. The second end of the third inductor is connected to one side of the capacitor, and the other side of the capacitor is grounded.

The first, second, and third inductors prevent the inductance L ′ = ESL + L ₃ −M ₁₂ −M ₂₃ + M ₁₃ from becoming too small due to the mutual inductance M ₁₃ between the first and third inductors. Selected and positioned relative to each other. In practice, the overall efficiency of the common-mode noise filter is improved by minimizing the inductances L ′ and ESL through the connection between the first and second inductors and ground, and is shown by the graph 10 in FIG. It approaches the characteristics of an ideal filter.

  In one configuration, the wire is wound around a magnetic structure such as a ring made of a ferromagnetic material. The second wire is electrically connected to the first wire by a tap adjacent to the load end of the wire, and then the second wire is also wound around the magnetic structure and then electrically connected to the load end. Connected to. The third wire begins with a tap between the first and second wires and travels around the magnetic structure along the second wire. The third wire is then connected to the capacitor.

First wire between the electrical tap is on a wire wound as a noise source, first to form an inductor L _1, a wire to the load from the tap form a second inductor L _2. The third inductor L ₃ provided by the third wire further runs in parallel closely adjacent to the second inductor, such that the second and third inductors are well coupled by mutual inductance. So positioned.

All three inductors exhibit mutual inductance with respect to each other. For example, M ₁₂ is the mutual inductance between the first and second inductors, M ₂₃ is the mutual inductance between the second and third inductors, M ₁₃ is the mutual inductance between the first and third inductors It is. The inductances are coupled together and the polarity is also shown in FIG.

As a result, the inductance of the path from the junction of the first and second inductors to the capacitor is equal to L ₃ −M ₁₂ −M ₂₃ + M ₁₃ where the size of the third inductor is L ₃ . Ideally, this inductance is equal to the negative ESL for the capacitor, and therefore more closely approximates an ideal filter. In general, L ₁ and L ₂ should be large to prevent high frequency current from traveling between the source and the load, thereby increasing M ₁₂ and M _{23 as} well. ESL is much smaller than _{usual, M 12} and _{M 23.} However, L ₃ and M ₁₃ can prevent L ₃ −M ₁₂ −M ₂₃ + M ₁₃ from becoming too small relative to ESL.

  The filter of the present invention is particularly useful for use as a common mode noise filter, but may be used as a differential noise filter with ESL cancellation if one side of the common mode filter is simply a ground line.

  A better understanding of the present invention will be obtained when the following detailed description is read in conjunction with the accompanying drawings, in which: Like reference symbols refer to like parts throughout the several views.

It is a graph which shows the characteristic of an ideal filter and an actual filter. FIG. 2 is a side view and a partial schematic diagram illustrating a preferred embodiment of a noise filter. It is the schematic which shows the circuit diagram of a noise filter. It is a figure which shows the equivalent circuit of FIG. 3 in which each voltage difference between terminals is mutually equivalent. It is a perspective view which shows the structure of a noise filter. FIG. 5 is another perspective view showing the structure of a noise filter including additional inductance that tunes the total inductance to zero.

  Referring initially to FIGS. 2 and 3, noise filter 20 is shown interconnected between an electrical noise source 22 such as a hybrid or electric vehicle inverter and a load 24 such as an electric or hybrid vehicle battery. Has been. The noise filter 20 is preferably positioned in close proximity to the electrical noise source 22.

  The noise filter 20 includes a magnetic structure 26 such as a ferrite bead. Wires 28 and 30 carry common mode noise current from noise source 22 to load 24. A ground 32 such as a vehicle frame is also associated with the noise filter 20.

  Both wires 28 and 30 between the noise source 22 and the load are wound around the magnetic structure 26. In addition, the two wires 28 and 30 are wound around the magnetic structure 26 in the same manner and associated with the same components. Therefore, only the design and components associated with wire 28 will be described in detail. The same description also applies to the winding of the wire 30.

  Referring again to FIGS. 2 and 3, the wire 28 extends from the noise source 22 and is wound around the magnetic structure 26 with a certain number of turns and then connected to the load 24. However, a wire tap 34 is formed on the wire 28 at an intermediate point along the portion of the wire 28 wound around the magnetic structure 26. Further, the tap 34 is positioned closer to the load 24 than the noise source 22.

The tap 34 effectively divides the turns of the first wire 28 around the magnetic structure 26 into _two inductors L ₁ and L ₂ . Inductor L ₁ and L ₂ are connected to each other in series between each source of noise 22 and the load 24. Furthermore, the magnitude of the inductance of L ₁ is greater than the inductance of the inductor L _2.

The second wire 36 is electrically connected to the tap 34 is a junction point between the inductors L ₁ and L _2. This wire 36 is wound around the magnetic structure 26 to form a _third inductor L3. The third inductor L ₃ is further closely positioned adjacent to the second inductor L _2, as a result, mutual inductance between the inductors L ₂ and L ₃ are increased. Therefore, the inductor L ₃ is, itself is canceled, it wounds to cause a negative inductance relative to the inductance of the inductor L ₁ and L _2.

Next, the wire 36 is connected to one side of the capacitor 40 and the other side of the capacitor 40 is electrically connected to the ground 32. Capacitor 40 exhibits a parasitic inductance ESL in conjunction with its associated wire 36 and connection to ground 32. Ideally, the inductance L′−ESL = 0, so that the first inductor L ₁ and the second inductor L ₂ and the tap 34 between the ground 32 and the capacitor 40 are approximated to an ideal noise filter. The series inductance of the capacitance of the equivalent circuit is equal to zero.

However, the three inductors L ₁ , L ₂ , and L ₃ are each affected by the mutual inductance from the other two inductors. Therefore, assume an equivalent circuit of three branches L _x , L _y , and L _z of the equivalent inductance of FIG. The values of the three branches L _x , L _y , and L _z of the filter are calculated as:
L _x = L ₁ + M ₁₂ + M ₂₃ + M ₁₃
L _y = L ₂ + M ₁₂ −M ₂₃ −M _{13
L z = L 3 + M 12} -M 23 + M 13
In the formula, M is a mutual inductance.

FIG. 5 shows the design of FIG. Wire 28 is wound around a ferromagnetic block having one hole. The tap 34 is on the wire 28 on the side of the terminal _Tp1 . Wire 36 enters the hole in the ferromagnetic block and is positioned near the wire segment between tap 34 and T _{p2 of} wire 28. In this configuration, each polarity of mutual inductance corresponds to that of FIG.

Ideally, L _z -ESL is equal to zero. In practical applications, the filter adjusts the number of turns of inductors L ₁ , L ₂ , and / or L ₃ , as well as the length of the magnetic path of inductors L ₁ and L ₂ on magnetic structure 26. by adjusting the width, by adjusting the mutual inductance M ₁₂ between the inductors L ₁ and L _2, it may be tuned.

Referring now to FIG. 6, an alternative design for _three inductors L ₁ , L ₂ , and L ₃ is shown. In each case, the inductor includes a winding. FIG. 6 also shows a compensation inductor L _c that tunes L _z such that L _z + L _c −ESL = 0. In FIG. 6, L _c has a winding axis that is orthogonal to L _x , L _y , and L _z . Therefore, even when L _c is close to other inductors, the mutual inductance between L _c and the other becomes even smaller and independent of the other inductances. Therefore, it is easy to select the value of L _c.

  From the above it can be seen that the present invention provides a simple but very effective common mode noise filter. The common-mode noise filter concept may be used to reduce noise in differential-mode electron currents, but has been found to be very effective in reducing common-mode noise.

  While the invention has been described, many variations to the invention will become apparent to those skilled in the art without departing from the spirit of the invention as defined by the scope of the appended claims.

Claims (8)

First and second inductors respectively connected in series between the noise source and the load;
A capacitor exhibiting parasitic inductance,
A first end connected to the junction of the first and second inductors, and a second end connected to one side of the capacitor, the other side of the capacitor being grounded A third inductor connected,
The mutual inductance between the first and second inductors is subtracted from the parasitic inductance of the capacitor and the inductance of the third inductor, and the mutual inductance between the second and third inductors is subtracted. A noise source and a load, wherein the first, second, and third inductors are selected and positioned relative to each other such that the difference between the two inductors plus the mutual inductance is minimized. Common-mode noise filter adapted to connect in series between.   The common-mode noise filter of claim 1, wherein the first, second, and third inductors are wound on a common magnetic structure.   The common-mode noise filter of claim 2, wherein the magnetic structure includes a ring.   The common-mode noise filter of claim 1, wherein the first, second, and third inductors each include a turn on a magnetic structure.   The common-mode noise filter of claim 4, wherein the third inductor is wound in close proximity to the second inductor.   The first and second inductors include turns on a magnetic structure, and the first end of the third inductor includes a tap at an intermediate point on the turns. Common-mode noise filter.   The common-mode noise filter of claim 1, wherein the value of the first inductor is greater than both the second and third inductors.   The first, second, and third inductors each include turns about an axis, and an axis of an additional compensating inductor is perpendicular to the axes of the first, second, and third inductors The common-mode noise filter according to claim 1.

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